These are some of the mxing tools that I've tested and used so far.
TRAKTOR 3 is a versatile and comprehensive digital DJing solution designed to meet the most professional of standards.
The Scratch LIVE interface connects almost any computer to an ordinary pair of turntables or CD players, and the software faithfully tracks every subtle movement of the stylus on the included control records. The same movement is then instantly applied to any digital audio file in the user's collection producing a sound and feel that is indistinguishable from vinyl.
Running natively on Windows XP and Mac OS X, the software has all the features of a modern DJ player, including beat extraction, real time tempo metering, waveform coloring based on spectral content, multiple cue points per track, and full iTunes library integration. Tailored for performance work, tracks are rapidly located via full text search of ID3 tags, or even recorded directly from a microphone, and assigned to turntable control with a single key press.
Mixmeister is a powerful tool that you can use to create a professional-sounding mix from your music files with a minimum of effort. Express is used every day by dance music fans, party DJs, fitness instructors and choreographers who want to "let the computer do the hard parts" and make their own mix CD in minutes. This software is not suitable for live mixing (although I've already seen some DJ's using it in clubs).
Are there any other programs you'd like to recommend?